• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.17 no.2
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• pp.103-113
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• 2013

We analyze the queueing model for leaky bucket (LB) scheme with dynamic arrivals and token rates. In other words, in our LB scheme the arrivals and token rates are changed according to the buffer occupancy. In telecommunication networks, the LB scheme has been used as a policing function to prevent congestion. By considering bursty and correlated properties of input traffic, the arrivals are assumed to follow a Markov-modulated Poisson process (MMPP). We derive the distribution of system state, and obtain the loss probability and the mean waiting time. The analysis is done by using the embedded Markov chain and supplementary variable method. We also present some numerical examples to show the effect of our proposed model.

• Journal of Distribution Science
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• v.19 no.11
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• pp.59-68
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• 2021

Purpose: The Covid-19 pandemic has had excessively severe impacts on all the nodes and edges of any supply chain due to changes in consumer behaviours and lockdown restrictions from governments among countries. This article aims to provide a simulating experiment on how a supply chain deals with supply disruption risks by flexibility in the inventory level of each sector as a buffer considering the overall cost to fulfil demand in the market. Research design, data and methodology: Agent-based simulation techniques are used to determine the cost-efficiency and customer waiting time related to varying inventory levels of each member in the supply chain when using inventory buffers. Findings: This study has shown that any sudden changes in the inventory level of each sector are likely to impact the rest of the supply chain. Among all sectors, the wholesaler will be impacted more severely than others. Also, the manufacturing sector is the most suitable node to adjust inventory depending on its manufacturing ability. Conclusion: The findings of the study provide insightful implications for decision-makers to adjust inventory levels and policymakers to maintain manufacturing activities in the context of the pandemic restrictions to deal with the excessive demand and potential supply disruption risks.

• Health Policy and Management
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• v.14 no.3
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• pp.20-44
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• 2004

The National Health Insurance Expenditure has been increased rapidly since the introduction of the separation of prescription and dispensing in 2000, and this trend of rapid growth in overall spendings rate has been observed predominantly among medical practitioners. This study was conducted to investigate the growth rate and distributional changes in private medical practitioners' expenses from 1999 to 2002 and its determinants using the National Health Insurance claims data. The total increasing rate of all medical practitioners' expenditure paid by the National Health Insurance between 1999 and 2002 was $41.71\%$, which exceeding that of general hospitals by $20\%$p. But the income distribution among each practitioner was improved as the changes in Gini coefficient(from 0.40 to 0.38) and decile distribution ratio(from 0.25 to 0.29) during the same period showed. However, this improvement in distributional patterns is not enough since even in 2002 it turned out that the highest $10\%$ income group earned 33times more than the lowest $10\%$ income group did. Also, higher Gini coefficient was observed in larger cities and some department like plastic surgery, obstetrics and gynecology. The major causes of this differentials in medical practitioners' expenses were factors related to medical demand like proportion of old population, residential economic status in a given area. In addition, providers' economic incentives also played an important role in determining their income distribution. The large income differentials among physicians may imply a skewed distribution of patients and thus long waiting time, inefficient utilization of resources and potential inadequate quality of care. In this sense, unreasonable distributional gaps should be reduced, so effective measures as well as ongoing monitoring would be necessary to correct current distributional problems.

• Journal of KIISE:Computer Systems and Theory
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• v.26 no.9
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• pp.1073-1082
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• 1999

본 논문에서는 시스템 내의 프로세서들을 효과적으로 사용하기 위한 적응적 프로세서 할당 정책을 제안한다. 프로그램의 병렬성을 향상시키기 위하여 일반적으로 병렬 처리에 사용될 프로세서 개수를 증가시킨다. 그러나 증가된 프로세서들은 그레인 크기에 변화를 일으키며 이는 캐쉬 성능에 영향을 미친다. 특히 대역이 제한된 공유 버스를 사용하는 시스템에서는 프로세서 개수의 증가는 공유 버스에 대한 접근 경쟁을 크게 증가하므로 버스에서 대기하는 시간이 프로세서 증가에 의한 계산 능력 이득을 상쇄시키는 주요한 원인이 되고 있다. 본 논문에서 제안한 적응적 프로세서 할당 정책은 프로그램이 수행되는 도중에 임의의 기간동안 공유버스에 대기중인 프로세서 분포에 관한 정보를 얻는다. 그리고 이 정보를 바탕으로 프로세서 개수를 변경하는 방법이다. 모의 시험에서 적응적 프로세서 할당 정책은 프로그램들의 버스 트래픽 특성에 따른 최적의 적합한 프로세서 개수를 발견함을 보인다. 그리고 적응적 프로세서 할당 정책은 고정된 프로세서 개수를 사용한 가장 좋은 성능보다는 다소 떨어진 성능을 나타내었으나 시스템의 프로세서 활용성을 높여 효과적 시스템 사용에 기여함을 보인다. Abstract In this paper, the adaptive processor allocation policy is suggested to make effective use of processors in system. To enhance the parallelism, the number of processors used in the parallel computing may be increased. However, increasing the number of processors affects the grain size of the parallel program. Therefore, it affects the cache performance. In particular, when the shared bus is employed, since increasing the number of processors can result in a significant amount of contention to achieve the shared-bus, the increased computing power is offset by the bus waiting time due to these contentions. The adaptive processor allocation policy acquires the information about the distribution of waiting processors on shared bus for any execution period of programs. And it changes the number of processors working in parallel processing during the program's run. Our simulation results show that the adaptive processor allocation policy finds the optimum feasible number of processors based on the bus traffic characteristic of programs. Thus, it contributes to effective system utilization, even though it performs slightly less efficiently than using a fixed number of processors with the best performance.

• Journal of the Korean Institute of Navigation
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• v.13 no.3
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• pp.37-44
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• 1989

Recently recognize the labor productivity of port physical distribution system in the port and shipping areas, Much Efforts for evaluating this productivity has been made continuously. BUt still there is little study, so far, on a systematic research for the management of port labor gangs, and even those were mainly depended on a rule of thumb. Especially the object of this study is to introduce the method of optimal allocation and assignment for the labor gangs per pier unit in the multiple ships berthed at an arbitary pier or port. In case the multiple ships have a homogeneous cargoes or do not have sufficient labor gangs to be assigned. The problem of optimal allocation and assignment of the labor gangs to be i) formalized with multi-state decision process in form of difference equation as the pattern which converted the independent multiple ships into a single ship with the intra-multiple ships, and ii) the optimal size of labor gangs could be obtained through the simple mathematical method instead of complicated dynamic programming, and iii) In case of shortage of labor gangs available the evaluation function considering the labor gangs available and total shift times was introduced, and iv) the optimal allocation and assignment of labor gangs was dealt at the point of minimizing the summation of the total shift times and at the point of minimizing the total cost charged for the extra waiting time except PHI time during port times for the multiple ships combinations.

• The Journal of Korea Robotics Society
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• v.15 no.2
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• pp.100-106
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• 2020

In the agricultural field, interests in research using robots for fruit harvesting are continuously increasing. Dual arm manipulators are promising because of its abilities like task-distribution and role-sharing. To operate it efficiently, the task sequence must be planned adequately. In our previous study, a collision-free path planning method based on a genetic algorithm is proposed for dual arm manipulators doing tasks cooperatively. However, in order to simplify the complicated collision-check problem, the movement between tasks of two robots should be synchronized, and thus there is a problem that the robots must wait and resume their movement. In this paper, we propose a heuristic algorithm that can reduce the total time of the optimal solution obtained by using the previously proposed genetic algorithm. It iteratively desynchronizes the task sequence of two robots and reduces the waiting time. For evaluation, the proposed algorithm is applied to the same work as the previous study. As a result, we can obtain a faster solution having 22.57 s than that of the previous study having 24.081 s. It will be further studied to apply the proposed algorithm to the fruit harvesting.

• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.24-31
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• 2015

효소는 생명 현상을 구현하는 단백질 촉매인데 그 동안 효소의 촉매 반응 속도는 Michaelis-Menten(MM) 모델로 대부분 설명되어 왔다. 그러나 MM 모델은 실험으로 측정된 단일 효소 반응시간의 확률분포 모양을 설명할 수 없다. MM 모델에 반응계수의 정적 무질서 개념을 도입한 효소 반응 모델도 기질 농도에 따라 변화하는 효소 반응시간의 통계적 요동을 설명하지 못한다. 우리는 단일 효소 반응시간의 통계적 요동이 기질에 따라 변화하는 양상을 설명하기 위해 효소 반응을 구성하는 개별 화학반응을 단순히 푸아송 과정이 아닌 갱신과정(renewal process)으로 확장한 효소 반응 모델을 제안한다. 우리는 이 단일 효소 반응 모델과 기질에 따른 효소 반응시간 분산 변화 데이터를 비교하여 효소-기질 복합체의 지속시간 분포를 간단한 형태로 얻어내었다. 또한, 이 정보를 토대로 전산모사를 수행하여 효소 반응시간의 확률분포를 얻어내고, 실제 실험 결과 및 기존 이론들과 비교하였다. 뿐만 아니라 단일 효소 반응시간의 확률분포를 연속 시간 임의의 보행자(continuous time random walker)의 대기시간 확률분포(waiting time distribution)로 대응하면, 평균 제곱 변위가 시간에 따라 단순히 증가 하지 않는 고분자의 특이 수송(anomalous diffusion) 현상도 정량적으로 설명할 수 있었다.

• The KIPS Transactions:PartD
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• v.16D no.3
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• pp.339-352
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• 2009

There are a number of formal methods for distributed real-time systems in ubiquitous computing to analyze and verify the behavioral, temporal and the spatial properties of the systems. However most of the methods reveal structural and fundamental limitations of complexity due to mixture of spatial and behavioral representations. Further temporal specification makes the complexity more complicate. In order to overcome the limitations, this paper presents a new formal method, called Timed Calculus of Abstract Real-Time Distribution, Mobility and Interaction(t-CARDMI). t-CARDMI separates spatial representation from behavioral representation to simplify the complexity. Further temporal specification is permitted only in the behavioral representation to make the complexity less complicate. The distinctive features of the temporal properties in t-CARDMI include waiting time, execution time, deadline, timeout action, periodic action, etc. both in movement and interaction behaviors. For analysis and verification of spatial and temporal properties of the systems in specification, t-CARDMI presents Timed Action Graph (TAG), where the spatial and temporal properties are visually represented in a two-dimensional diagram with the pictorial distribution of movements and interactions. t-CARDMI can be considered to be one of the most innovative formal methods in distributed real-time systems in ubiquitous computing to specify, analyze and verify the spatial, behavioral and the temporal properties of the systems very efficiently and effectively. The paper presents the formal syntax and semantics of t-CARDMI with a tool, called SAVE, for a ubiquitous healthcare application.

• Journal of the Korea Safety Management & Science
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• v.19 no.3
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• pp.129-135
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• 2017

The respective delivering vehicle loaded with the own cargo moves into the respective delivery area. At the base, the delivery points D1 and D2, for example, have the same starting point but the destination is different. The average delivering time of the delivery vehicle is mostly more than 8 hours a day. Therefore, the efficiency of delivery is generally low. In this study, the deliveries will be forwarded from a base station to a delivery point where cross docking will be applied to a single vehicle, and will be distributed from the cross docking point through cross docking. If the distribution is implemented, one vehicle will not have to be operated from the base to the cross docking point. In that case, logistics cost will be reasonably saved by the reduction of transportation cost and labor time. If one vehicle only runs from the base to the cross docking point, each vehicle will be operated in two shifts, and the vehicle operation can be efficiently implemented. This research model is based on the assumption that the 3 types of ratios between the traffic volume of the vehicles starting at the base and the vehicles waiting at the cross docking point are set to the first ratio of 30% to 70%, the second ratio of 50% to 50% and the final ratio of 70% to 30%. As a result of the study, The delivery time in the cross docking point is much higher than that in present on the condition that the cargo volume in the D2 area is more than 50%. Likewise, the delivery time is slightly higher on the condition that the cargo volume is less than 50%. Time is reduced in terms of 50% model like AS-IS model.

• Management Science and Financial Engineering
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• v.20 no.2
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• pp.27-31
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• 2014

This paper studies the assortment optimization problem in online retailing by using a multinomial logit model in order to take consumer choice behavior into account. We focus on two unique features of online purchase behavior: first, there exists increased amount of uncertainty (e.g., size and color of merchandize) in online shopping as customers cannot experience merchandize directly. This uncertainty is captured by the scale parameter of a Gumbel distribution; second, online shopping entails unique shopping-related disutility (e.g., waiting time for delivery and security concerns) compared to offline shopping. This disutility is controlled by the changes in the observed part of utility function in our model. The impact of changes in uncertainty and disutility on the expected profit does not exhibit obvious structure: the expected profit may increase or decrease depending on the assortment. However, by analyzing the structure of the optimal assortment based on convexity property of the profit function, we show that the cardinality of the optimal assortment decreases and the maximum expected profit increases as uncertainty or disutility decreases. Therefore, our study suggests that it is important for managers of online retailing to reduce uncertainty and disutility involved in online purchase process.